The legendary sword Excalibur, the magic sword of King Arthur. Arthur became king because he, alone, could remove Excalibur from a stone in which it was captive, thus proving that he was the true heir to the throne.

Excalibur's presence in the Phantom's Treasure Room is probably the only extant proof that King Arthur really existed. The only other tangible evidence was discovered in the 14th century, and has since vanished. At that time, a grave was unearthed on the grounds of the great monastery in Glastonbury, England (a site within earshot of the sacred well where the Holy Grail is said to have been buried by Jesus' uncle, Joseph of Arimathea). The grave contained the skeletons of a very tall man and a petite, delicate, woman. With them was a lead cross bearing an inscription identifying this as King Arthur and Queen Guinevere. King Edward II came to Glastonbury to witness the re-burial of the remains, whose location has now been lost. The cross passed through different hands for centuries, until it was finally auctioned to an unknown buyer in the 1930's, and its whereabouts have been unknown since.

The Phantom regards Excalibur, and the other historically significant items articles in the treasure-room, as a sacred trust, to be guarded for the sake of posterity.